Another Avengers 4 fan theory suggests star Zoe Saldana's costume proves time travel will play a big part the upcoming Marvel Studios sequel.

The suggestion is that a behind-the-scenes shot of the Guardians of the Galaxy star in her Gamora costume may have spoiled Joe and Anthony Russo's big twist.

Reddit user SuperheroNick noticed that Saldana's outfit matches what she wore in 2014's Guardians of the Galaxy rather than in Avengers: Infinity War. Taken during the filming of Avengers 4, the photo seems to suggest either a flashback or a time-travel scene. That also links to a post from December showing Saldana in the makeup chair for her Gamora transformation, and wearing her Guardians of the Galaxy outfit.

Saldana's makeup post made waves, as it confirmed Gamora returns in Avengers 4, so many will have missed that she has worn the outfit before. Looking back, Saldana's costume is definitely different to what she wore in both Guardians of the Galaxy Vol. 2 and Infinity War.

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Gamora was one of Infinity War'scasualties, and only a select few know what role the character will have in Avengers 4. Although Gamora is expected to return in some form, a scene that includes the green-skinned daughter of Thanos following her death would surely feature her Infinity War costume. Returning to her original Guardians outfit is particularly specific.

Why the remaining Avengers would travel back to the events of Guardians of the Galaxy is a mystery, but considering the purple Power Stone was a major part of that film, the team could try and claim the Infinity Stones before Thanos does.

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After an old Avengers 4 set photo first sparked the time travel theories, more and more evidence has come to light. As well as Saldana's possible spoiler, remember that one photo appeared to recreate Loki's attack on New York from 2012's The Avengers. Whatever happens in Avengers 4, it looks like the movie will be a trip down memory lane.

While even Ant-Man and the Wasp's Peyton Reed refuses to rule out time travel, fans will have to wait until next year to find out how the Russo brothers intend wrap up Phase Three of the MCU.

Directed by Joe and Anthony Russo, Avengers 4 stars Robert Downey Jr., Chris Evans, Chris Hemsworth, Brie Larson, Mark Ruffalo, Jeremy Renner, Scarlett Johansson, Paul Bettany, Anthony Mackie, Paul Rudd, Elizabeth Olsen, Tom Holland, Benedict Cumberbatch, Chadwick Boseman, Chris Pratt, Zoe Saldana, Dave Bautista, Bradley Cooper, Vin Diesel, Karen Gillan, Evangeline Lilly, and Josh Brolin. The film is set to hit theaters on May 3, 2019.